1. Field of the Invention
This invention relates broadly to self-propelled projectiles. More particularly, this invention relates to rockets powered by hybrid propellant systems.
2. State of the Art
Rocket boosters (motors) generally fall into three classes: solid propellant boosters in which a solid fuel element, or grain, undergoes combustion to produce thrust that propels the rocket, liquid propellant boosters that accomplish the same function with a liquid fuel material, and hybrid boosters, described below. Solid and liquid rocket boosters can produce relatively large amounts of thrust, but for a relatively short amount of time. In addition, solid and liquid rocket boosters are generally expensive to develop and produce due to the inherent dangers of the highly combustible solid fuels.
Hybrid rocket boosters are described in detail in co-owned U.S. Pat. No. 5,715,675 to Smith et al., which is hereby incorporated by reference herein in its entirety. They have been characterized as a cross between a solid propellant booster and a liquid propellant booster. Generally hybrid boosters use a fluid reactant (an oxidizer) to burn a solid fuel element, although they may use a combustible liquid fuel and a solid reactant. The hybrid rocket propellant (fuel and reactant together) can be ignited by an igniter, such as an electrically-generated spark, by pyrotechnic means, or by initial injection of an ignition fluid which exothermically reacts with the fuel or reactant. The fuel of a hybrid rocket is inert until mixed with the oxidizer in the presence of an igniter in a combustion chamber. As such, there is no danger of inadvertent and uncontrollable combustion.
When the propellant is combusted, the oxidizer must be injected at a relatively high pressure along the surface of the solid reactant to provide the necessary thrust level. The pressure to inject the oxidizer is created by storing the fluid reactant at a relatively high pressure, e.g., 1000 psi, in a tank. Of course, a tank capable of withstanding 1000 psi must have relatively thick walls and is therefore extremely heavy. The weight of the fluid tank influences rocket flight time and distance traveled.
It is therefore an object of the invention to provide a hybrid rocket motor which uses a storage tank with relatively thinner walls.
It is also an object of the invention to provide a hybrid rocket motor which stores fluid reactant at relatively low pressures.
It is another object of the invention to provide a hybrid rocket motor which uses a relatively light weight fluid reactant tank.
It is a further object of the invention to provide a hybrid rocket motor which injects fluid reactant into a combustion chamber at a relatively high pressure.
In accord with these objects, which will be discussed in detail below, a hybrid motor includes a storage tank which stores fluid reactant (oxidizer) under relatively low pressure, e.g., 100 psi, a turbopump preferably directly coupled to an outlet of the storage tank which pressurizes the oxidizer to a relatively high pressure, e.g., 1000 psi, a combustion chamber including a solid fuel, and an injector between the turbopump and combustion chamber through which the oxidizer is injected into the combustion chamber. According to a preferred aspect of the invention, the turbopump is operated by expanded gas from a heat exchanger in an expander cycle. According to another preferred aspect of the invention, the fluid flowing through the heat exchanger is the same fluid as the fluid reactant, and more preferably is oxidizer tapped from the storage tank. A barrier is maintained between a fluid reactant feed line from the turbopump and the injector until sufficient pressure is created by the turbopump to pump the fluid reactant at the requisite pressure into the injector.
A rocket is also provided which incorporates the hybrid motor. The rocket includes a nose cone at the fore end, a rear nozzle, and a casing about the hybrid motor.
Additional objects and advantages of the invention will become apparent to those skilled in the art upon reference to the detailed description taken in conjunction with the provided figures.